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<Title>PropertyGraph</Title>
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<H2><A NAME="concept:PropertyGraph"></A>
PropertyGraph
</H2>

A PropertyGraph is a graph that has some property associated with each
of the vertices or edges in the graph. As a given graph may have
several properties associated with each vertex or edge, a tag is used
to identify which property is being accessed.  The graph provides a
function which returns a property map object.

<P>

<H3>Refinement of</H3>

<a href="./Graph.html">Graph</a>

<h3>Notation</h3>

<Table>
<TR>
<TD><tt>G</tt></TD>
<TD>A type that is a model of PropertyGraph.</TD>
</TR>

<TR>
<TD><tt>g</tt></TD>
<TD>An object of type <tt>G</tt>.</TD>
</TR>

<TR>
<TD><tt>X</tt></TD>
<TD>Either the vertex or edge descriptor type for <tt>G</tt>.</TD>
</TR>

<TR>
<TD><tt>x</tt></TD>
<TD>An object of type <tt>X</tt>.</TD>
</TR>


<TR>
<TD><tt>Map</tt></TD>
<TD>The type <tt>boost::property_map&lt;G, Property&gt;::const_type</tt>.</TD>
</TR>

<TR>
<TD><tt>v</tt></TD>
<TD>An object of type <tt>boost::property_traits&lt;Map&gt;::value_type</tt>.</TD>
</TR>

<TR>
<TD><tt>PropertyTag</tt></TD>
<TD>A type that models the <a href="./PropertyTag.html">PropertyTag</a> concept.</TD>
</TR>

<TR>
<TD><tt>p</tt></TD>
<TD>An object of type <tt>PropertyTag</tt>.</td>
</TR>

<TR>
<TD><tt>pmap</tt></TD>
<TD>An object of type <tt>Map</tt>.</td>
</TR>

</table>

<H3>Associated types</H3>

<table border>

<tr>
<td><pre>boost::property_map&lt;G, PropertyTag&gt;::type</pre>
The type of the property map for the property specified by
<TT>PropertyTag</TT>.  This type must be a model of <a
href="../../property_map/doc/ReadWritePropertyMap.html">ReadWritePropertyMap</a> 
with a key type the same as the graph's vertex or edge descriptor type.
</td>
</tr>

<tr>
<td><pre>boost::property_map&lt;G, PropertyTag&gt;::const_type</pre>
The type of the const property map for the property specified by
<TT>PropertyTag</TT>. This type must be a model of <a
href="../../property_map/doc/ReadablePropertyMap.html">ReadablePropertyMap</a>
with a key type the same as the graph's vertex or edge descriptor type.
</td>
</tr>

</table>

<h3>Valid Expressions</h3>

<table border>

<tr>
<td> <TT>get(p,&nbsp;g)</TT> </td>
<td>
Returns the property map for the property specified by the
<tt>PropertyTag</tt> type. The object <tt>p</tt> is only used to
carry the type.<br>
Return type: <TT>boost::property_map&lt;G,&nbsp;PropertyTag&gt;::type</TT> if <TT>g</TT> is mutable and <br><TT>boost::property_map&lt;G,&nbsp;PropertyTag&gt;::const_type</TT> otherwise.
</td>
</TR>

<tr>
<td> <TT>get(p,&nbsp;g,&nbsp;x)</TT> </td>
<td>
Returns the property value (specified by the <tt>PropertyTag</tt> type)
associated with object <tt>x</tt> (a vertex or edge).
The object <tt>p</tt> is only used to carry the type.
This function is equivalent to:<br>
<tt>get(get(p, g), x)</tt><br>
Return type: <tt>boost::property_traits&lt;Map&gt;::value_type</tt>
</td>
</TR>

<tr>
<td> <TT>put(p,&nbsp;g,&nbsp;x,&nbsp;v)</TT> </td>
<td>
Set the property (specified by the <tt>PropertyTag</tt> type)
associated with object <tt>x</tt> (a vertex or edge) to
the value <tt>v</tt>. The object <tt>p</tt> is only used to carry the type.
This function is equivalent to:<br>
<tt>
pmap = get(p, g);<br>
put(pmap, x, v)
</tt><br>
Return type: <TT>void</TT>
</td>
</TR>


</TABLE>

<H3>Complexity</H3>

The <tt>get()</tt> property map function must be constant time.


<H3>Models</H3>


<UL>
<LI><tt>adjacency_list</tt> with <tt>VertexProperty=property&lt;vertex_distance_t,int,property&lt;vertex_in_degree_t,int&gt; &gt;</tt> and <tt>PropertyTag=vertex_distance_t</tt>.</li>
<li><tt>adjacency_list</tt> with <tt>VertexPropertyTag=property&lt;vertex_distance_t,int,property&lt;vertex_in_degree_t,int&gt; &gt;</TT> and <tt>PropertyTag=vertex_in_degree_t</tt>.</li>
</UL>


<H3>Concept Checking Class</H3>

<PRE>
  template &lt;class Graph, class X, class PropertyTag&gt;
  struct PropertyGraphConcept
  {
    typedef typename property_map&lt;G, PropertyTag&gt;::type Map;
    typedef typename property_map&lt;G, PropertyTag&gt;::const_type const_Map;
    void constraints() {
      function_requires&lt; GraphConcept&lt;G&gt; &gt;();
      function_requires&lt; ReadWritePropertyMapConcept&lt;Map, X&gt; &gt;();
      function_requires&lt; ReadablePropertyMapConcept&lt;const_Map, X&gt; &gt;();

      Map pmap = get(PropertyTag(), g);
      pval = get(PropertyTag(), g, x);
      put(PropertyTag(), g, x, pval);
      ignore_unused_variable_warning(pmap);
    }
    void const_constraints(const G&amp; g) {
      const_Map pmap = get(PropertyTag(), g);
      pval = get(PropertyTag(), g, x);
      ignore_unused_variable_warning(pmap);
    }
    G g;
    X x;
    typename property_traits&lt;Map&gt;::value_type pval;
  };
</PRE>


<h3>See Also</h3>

<a href="./property_map.html"><tt>property_map</tt></a>

<br>
<HR>
<TABLE>
<TR valign=top>
<TD nowrap>Copyright &copy; 2000-2001</TD><TD>
<A HREF="http://www.boost.org/people/jeremy_siek.htm">Jeremy Siek</A>, Indiana University (<A HREF="mailto:jsiek@osl.iu.edu">jsiek@osl.iu.edu</A>)
</TD></TR></TABLE>

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